When Richard Grossman, president of Tarrytown, N.Y.-based Gibraltar Management Co., surveyed the sidewalk outside his Middlesex Mall in South Plainfield, N.J., he saw its concrete sidewalk spalling and chipping and damaged from heat and frost.
Grossman feared he'd have to hire an outside crew to come in with jackhammers and tear up the 23-year-old sidewalk so it could be repoured with fresh concrete.
With 13,000 sq. ft. to repair, the prospect of the cost, the inconvenience to shoppers, and the inevitable loss of business from such a project was hardly appealing.
At the time, Middlesex Mall was undergoing an extensive interior renovation, and one of the products being used inside was a self-leveling concrete product by Corapolis, Pa.-based Ardex Inc. So Grossman asked the Ardex sales rep if a product was available to repair the outside sidewalk.
The answer was Ardex CD, an exterior concrete dressing that presented an alternative to tearing up and repouring the sidewalk. The product consists of a Portland cement base and special polymers that allow it to bond with existing concrete.
"This is a cosmetic dressing that is meant to be used over a concrete surface, not a structural or permanent installation," says David Fabyonic, national accounts director for Ardex, who compares the product to an asphalt sealer on a residential driveway.
Introduced about one year ago and launched nationally this past spring, Ardex CD was tested for about four years, undergoing freeze-thaw cycles and rock salt applications to simulate actual use. The testing shows that the product should last about three years under normal use, Fabyonic says.
Grossman decided to try Ardex CD on the sidewalk outside Middlesex Mall, as well as at a few other installations owned by Gibraltar. "I was prepared to tear the sidewalk out," he recalls. "It would have cost 10 times more."
Applying the concrete dressing The product works best when applied in a layer approximately 1/16" thick but can be applied up to 1" thick where spalls or gouges need to be filled in. Pigments - Ardex recommends iron oxide pigment - can be added directly to the mix.
Ardex CD comes in two forms, fine and coarse, with the fine texture best for interior applications and the coarse texture better for outdoor applications.
"The coarse texture has a rougher, broom finish, which is accomplished with a push broom. It helps to make a surface more slip-resistant," says Fabyonic.
The product has two mixing ratios: one for filling in spalls and gouges, called the patching ratio; and one for covering surfaces, the standard ratio. When filling in spalls, the mixture contains less water and is thicker, like a slurry. "You wait one hour after filling in the spalls and gouges, then put on a nice, even coat across the top at the regular mix ratio," Fabyonic advises.
Before adding pigments or choosing mix ratios, however, the surface must be properly prepared. Unlike some of the other Ardex flooring products, which can be used over ceramic tile, terrazzo or wooden floors, Ardex CD can be applied only over existing concrete.
In order for the product to bond, the surface must be clean - free of motor oil, chewing gum or anything else that could be a bond breaker.
"You need to prepare the surface by scraping it until you have something sound and solid," Fabyonic says. "Usually, a good power washer is sufficient, but when the surface is extremely damaged, you may need to use a shotblaster or a scarifier" - a tool that cuts into and rips the concrete.
The product is best applied with a steel trowel. Unlike the structural replacement of concrete floors or sidewalks, the procedure typically does not require an outside contractor. At Middlesex Mall, for instance, in-house maintenance and construction personnel performed the work of applying the concrete dressing.
The work does require precision and speed, however. "When you're adding the iron oxide pigments, you need to be careful to maintain the Ardex-to-water ratio," Fabyonic explains.
Once the proper amount of water is put in a bucket, the Ardex powder is slowly added while being mixed with a heavy-duty, hand-held electric drill that has a mixing paddle on the end. Mixing takes about two minutes.
"You have 15 minutes working time before the product starts setting," Fabyonic says. "It's important to maintain a wet edge when applying, so you would start with the second bag just where you left off with the first batch, and you'd keep maintaining that wet edge."
While a squeegee or a push broom can be used for the application, the steel trowel works best and yields maximum coverage, Fabyonic says. Each bag of Ardex CD yields 80 to 120 sq. ft. of coverage.
Sealer promotes durability Fabyonic recommends applying a breathable concrete sealer over the surface about 12 hours after the Ardex CD application.
"The surface should not have significant use until the sealer is applied," he says. "While the sealer isn't required, it will extend the life of the product."
The sealer must be breathable, he emphasizes, to allow moisture and air from the ground to rise up through the porous concrete and porous Ardex CD; an air-tight sealer would trap the moisture, resulting in damage to the concrete surface.
Surfaces treated with Ardex CD should be maintained like regular concrete. Depending on use, they may need to be resealed regularly.
The product can also be reapplied as needed, complete with power washing and sealing, because of the relative low cost involved, Fabyonic says.
As concrete flooring grows in popularity among shopping centers, both for indoor and outdoor applications, the demand for products like Ardex CD will no doubt increase. Other resurfacing products include chemical dressings such as epoxies that look like paint.
But at present, the real competition for concrete resurfacing is repouring the concrete itself. The introduction of innovative products to cover worn concrete provides cost-efficient alternatives to this process, allowing shopping centers to extend the life of their cement floors and sidewalks.